Age-dependent changes in intuitive and deliberative cooperation

Cooperation is one of the most advantageous strategies to have evolved in small- and large-scale human societies, often considered essential to their success or survival. We investigated how cooperation and the mechanisms influencing it change across the lifespan, by assessing cooperative choices from adolescence to old age (12–79 years, N = 382) forcing participants to decide either intuitively or deliberatively through the use of randomised time constraints. As determinants of these choices, we considered participants’ level of altruism, their reciprocity expectations, their optimism, their desire to be socially accepted, and their attitude toward risk. We found that intuitive decision-making favours cooperation, but only from age 20 when a shift occurs: whereas in young adults, intuition favours cooperation, in adolescents it is reflection that favours cooperation. Participants’ decisions were shown to be rooted in their expectations about other people’s cooperative behaviour and influenced by individuals’ level of optimism about their own future, revealing that the journey to the cooperative humans we become is shaped by reciprocity expectations and individual predispositions.

shows that females tended to cooperate slightly more than males.
Elicited risk aversion and a measure of desire for social acceptance were then added to specification (iii) as additional controls as follows = + * + * + * * _ + * + * (xiv) where denotes our elicited measure for certainty equivalents with high values denoting more aversion to risk, and where NB is our elicited measure of desire for social acceptance with high values denoting more desire. Table E1 shows that participants that were more risk averse and/or displayed more need for social acceptance tended to cooperate more.
An additional analysis carried out on the baseline PGG looked at the effects of predicted response times with each time condition (time-pressure vs time-delay). Such analysis consisted of a two-stage regression where predicted response times were first estimated conditional on the time condition and age (through a standard OLS regression), and PGG contributions were estimated using our baseline specification (iii) but replacing age with the predicted response times (to avoid collinearity problems), as follows = + * _ + * + * * _ (xv) where _ denotes the predicted response times. We relied on predicted response times rather than actual response times for this analysis as correlation between actual response times and Probit residuals might have otherwise violated exclusion restrictions. The first stage regression (omitted for sake of brevity here) established that individuals under time-pressure took on average 5.5 seconds to respond to the PGG task whereas those under time delay took on average 16.8 seconds to respond, with older individual spending surprisingly slightly less time on the task. The second stage Probit regression then established that within each condition, higher response times lead to significantly lower PGG contributions, as shown in Table E1.

Optimism, Age, PGG Contributions and Beliefs
The effect of optimism on PGG contributions and expected cooperation was also analyzed.
Simple OLS regressions established that optimism increased both variables as displayed in Table E2.
Further, age was shown to be positively associated with optimism as displayed in Table E3.   When the time condition was added to the regressions as in specification (viii), time-pressure was shown to consistently increase contributions across the five informational settings as shown in  implying that inequality in partners' contributions led to more sensitive responses than when partners behaved similarly. These results are reported in detail in Table E6.  Table   E7). Older participants were shown to be less responsive to information relative to younger ones. When responsiveness was added to the main Probit specification (iii) it was shown to increase PGG contributions as displayed by the ordered Probit regression in Table E8, meaning that participants whose contributions varied more across informational settings were those who had contributed more in the original uniformed PGG.
To conclude the analysis of conditional cooperation, we report results for our main specification (iii) but with the dependent variable, PGG, replaced by the informed contributions, Resp_x-y, to display the effect of age, time condition, and their interaction on conditional cooperation (see Table   E9). While the effect of age on contributions is consistent across the five informed settings, the effect of the time condition differs considerably across these and across age groups. Further, variability of parameter estimates was considerably increases in some of the informational settings. This is particularly evident in the informational case in which partners' contributions were low since several participants reduced their contributions considerably whereas others did not, making parameter estimates less precise.
Note. + p < .15, * p < .05, ** p < .01, *** p < .001. Table 10 reports results for the dictator game of the three key Probit specifications discussed in the main text. In contrast to the PGG, time-pressure had a more uniform effect on DG donations.

Dictator Game
Time-pressure raised DG donations consistently across age groups (except for adults for whom contributions were not affected by the time condition). Thus, intuitive reasoning consistently led to more altruism than reasoned choices supporting the view that altruism is an intuitive and deeply rooted trait of human behaviour (with the usual caveat, that in working-age adults intuitive and deliberative reasoning seem to coincide).
To understand the effect of altruism on PGG contributions, we then analysed two of our baseline specifications, but with DG donations added as a regressor, namely: = + * + * + * * _ + * (xvi) = + * + * + * * _ + * + * + * (xvii) When DG donations were added as a regressor to these specifications, donations became the main variable explaining PGG contributions dampening the effects of the other variables, as can be seen in Table E11. But these specifications also highlight a close association between cooperation and altruism, as measured in the PGG and DG.

Basic Data Checks
The following checks display key features of the sample and the data. Table E12 shows how the sample is split across the four age groups used in much of our empirical specifications. The sample of young adults is slightly larger than the rest, whereas the sample of adults is slightly smaller. The table also highlights that below age 30 the sample included significantly more female participants than male ones. Average age within age groups is also reported in the table. In the young adults group (those aged between 20 and 30) average age was only 22.9 revealing some skewness in the age distribution. Among older adults (those aged between 60 and 80) average age was 65.7 again revealing that our sample had more participants in their sixties than in their seventies.  Table E13 establishes that the sample was evenly split between time-pressure and time-delay groups. Further, it documents compliance with the time-pressure treatment by reporting response times quantile by quantile in both the time-pressure and the time-delay conditions. Only 7% of those in the time-pressure group did not comply with the treatment by taking more than 10 seconds to respond. Further, quantile by quantile, those in the time-pressure group took at least 10 seconds less to respond than those in the time-delay group. The slowest responders in the time-pressure group took on average 14 second less to respond than those in the same quantile of the time-delay group. Because of this, participants in the time-pressure group taking more than 10 seconds to respond were retained in the analysis. But results would not be affected by dropping them from the analysis.